1. Field of the Invention
The present invention relates to a low-bed type seismic isolator, which protects a seismic isolation object, such as an exhibit in a museum or the like, from an earthquake. Throughout the specification, the term "a seismic isolation object" is used to mean an object requiring a seismic isolator for protection from an earthquake.
2. Description of the Related Art
A conventional seismic isolator is constructed by X-rails 3 fixed to a lower plate 1 fixed to a foundation, Y-rails 4 which are fixed to the lower surface of an upper plate 2 above the X-rails 3 and which are disposed perpendicularly to the X-rails 3, and connection blocks 5 connecting the X-rails 3 and the Y-rails 4 together, as shown in FIG. 11. Although not shown in the drawing, a spring for restoration is required between the seismic isolator and the foundation. The connection block is arranged for movement such that a ball bearing is disposed on its lower portion to clamp the X-rail, whereas another ball bearing is disposed on its upper portion to clamp the Y-rail, and further a universal joint is provided at its central portion. A seismic isolation object 10 is placed on the seismic isolator, so that the height thereof is increased by an amount corresponding to the height of the seismic isolator. Therefore, if the seismic isolation object is a display case in a museum or the like, there may arise that a visitor whose eye-level is low in height, can not horizontally view an exhibit within the display case. Further, it is preferable to set the display case as low as possible from an aesthetic view point.